Human gets all information about the situations inside and outside his/her body through sensation and perception. The human brain has a region where the brain cells specially trained to perform the cognitive function. When the region is locally damaged, disorder occurs for each cognitive function.
The disorder of the cognitive function may occur due to various causes. Examples of the cognitive function disorder include cognitive function disorders caused by degenerative brain diseases including dementia, Parkinson's disease, stroke, Huntington's disease, etc., alcoholic cognitive function disorder, aging-induced cognitive function disorder, loss of brain function due to accidents, cognitive function disorder caused by cerebral hemorrhage, attention deficit hyperactivity disorder (ADHD), schizophrenia, and cognitive function disorder caused by chronic fatigue syndrome. Dementia, which is a representative degenerative brain disease, is a brain disease showing disorder of the overall cognitive function. It is usually caused by chronic or progressive brain diseases and exhibits a number of the so-called higher cerebral functions such as memory, thought, understanding, calculation, learning, language, judgment, etc. Also, as a degenerative change with aging, the brain function declines gradually, and as a result, cognitive ability declines.
Chronic fatigue syndrome (CFS) refers to prolonged severe fatigue with no known cause for at least 6 months and is commonly found in modern people. The chronic fatigue syndrome is characterized by severe fatigue which is not substantially rest and makes the patient very weak (United States Centers for Disease Control and Prevention, Fukuda et al. 1994).
The criteria for chronic fatigue syndrome include, together with fatigue, four or more of impaired memory or concentration, sore throat, tender lymph nodes, muscle pain, arthralgia, headaches of a new kind, unrefreshing sleep, post-exertional malaise, etc. And, symptoms commonly accompanied by the chronic fatigue syndrome include cognitive function decline such as concentration deficit, attention deficit and memory deficit. These symptoms suggest that chronic fatigue syndrome is accompanied by the disorder of the central nervous system. In addition, patients with chronic fatigue syndrome show signs of decreased brain blood flow in single-photon emission computed tomography (SPECT) more frequently than normal people or patients with depression.
Although no consistent results are reported on the neuropsychological examination of the cognitive function in chronic fatigue syndrome, recent studies show that the patients with chronic fatigue syndrome show significant decline in working memory and information processing.
The exact cause of chronic fatigue syndrome exhibiting such symptoms is not known and no medication is known that can permanently relieve the symptoms. In addition, many of the currently used drugs have mild adverse effects such as weariness, dizziness and nausea and severe adverse effects such as addiction and liver damage.
Therefore, development of a medicine that can treat cognitive function disorder and chronic fatigue syndrome without adverse effects is necessary. Because patients with chronic fatigue syndrome show signs of decreased brain blood flow in SPECT more frequently than normal people or patients with depression, if brain activity can be enhanced by increasing brain blood flow, it will be effective in treating chronic fatigue syndrome and improving accompanying symptoms.